path: root/fs/char_dev.c (plain)
blob: 417d77dcab917018eeaae30e3ab7389b7c8d53e5

1	/*
2	* linux/fs/char_dev.c
3	*
4	* Copyright (C) 1991, 1992 Linus Torvalds
5	*/
6
7	#include <linux/init.h>
8	#include <linux/fs.h>
9	#include <linux/kdev_t.h>
10	#include <linux/slab.h>
11	#include <linux/string.h>
12
13	#include <linux/major.h>
14	#include <linux/errno.h>
15	#include <linux/module.h>
16	#include <linux/seq_file.h>
17
18	#include <linux/kobject.h>
19	#include <linux/kobj_map.h>
20	#include <linux/cdev.h>
21	#include <linux/mutex.h>
22	#include <linux/backing-dev.h>
23	#include <linux/tty.h>
24
25	#include "internal.h"
26
27	static struct kobj_map *cdev_map;
28
29	static DEFINE_MUTEX(chrdevs_lock);
30
31	static struct char_device_struct {
32	struct char_device_struct *next;
33	unsigned int major;
34	unsigned int baseminor;
35	int minorct;
36	char name[64];
37	struct cdev *cdev; /* will die */
38	} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
39
40	/* index in the above */
41	static inline int major_to_index(unsigned major)
42	{
43	return major % CHRDEV_MAJOR_HASH_SIZE;
44	}
45
46	#ifdef CONFIG_PROC_FS
47
48	void chrdev_show(struct seq_file *f, off_t offset)
49	{
50	struct char_device_struct *cd;
51
52	if (offset < CHRDEV_MAJOR_HASH_SIZE) {
53	mutex_lock(&chrdevs_lock);
54	for (cd = chrdevs[offset]; cd; cd = cd->next)
55	seq_printf(f, "%3d %s\n", cd->major, cd->name);
56	mutex_unlock(&chrdevs_lock);
57	}
58	}
59
60	#endif /* CONFIG_PROC_FS */
61
62	static int find_dynamic_major(void)
63	{
64	int i;
65	struct char_device_struct *cd;
66
67	for (i = ARRAY_SIZE(chrdevs)-1; i > CHRDEV_MAJOR_DYN_END; i--) {
68	if (chrdevs[i] == NULL)
69	return i;
70	}
71
72	for (i = CHRDEV_MAJOR_DYN_EXT_START;
73	i > CHRDEV_MAJOR_DYN_EXT_END; i--) {
74	for (cd = chrdevs[major_to_index(i)]; cd; cd = cd->next)
75	if (cd->major == i)
76	break;
77
78	if (cd == NULL || cd->major != i)
79	return i;
80	}
81
82	return -EBUSY;
83	}
84
85	/*
86	* Register a single major with a specified minor range.
87	*
88	* If major == 0 this functions will dynamically allocate a major and return
89	* its number.
90	*
91	* If major > 0 this function will attempt to reserve the passed range of
92	* minors and will return zero on success.
93	*
94	* Returns a -ve errno on failure.
95	*/
96	static struct char_device_struct *
97	__register_chrdev_region(unsigned int major, unsigned int baseminor,
98	int minorct, const char *name)
99	{
100	struct char_device_struct *cd, **cp;
101	int ret = 0;
102	int i;
103
104	cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
105	if (cd == NULL)
106	return ERR_PTR(-ENOMEM);
107
108	mutex_lock(&chrdevs_lock);
109
110	if (major == 0) {
111	ret = find_dynamic_major();
112	if (ret < 0) {
113	pr_err("CHRDEV \"%s\" dynamic allocation region is full\n",
114	name);
115	goto out;
116	}
117	major = ret;
118	}
119
120	cd->major = major;
121	cd->baseminor = baseminor;
122	cd->minorct = minorct;
123	strlcpy(cd->name, name, sizeof(cd->name));
124
125	i = major_to_index(major);
126
127	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
128	if ((*cp)->major > major ||
129	((*cp)->major == major &&
130	(((*cp)->baseminor >= baseminor) ||
131	((*cp)->baseminor + (*cp)->minorct > baseminor))))
132	break;
133
134	/* Check for overlapping minor ranges. */
135	if (*cp && (*cp)->major == major) {
136	int old_min = (*cp)->baseminor;
137	int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
138	int new_min = baseminor;
139	int new_max = baseminor + minorct - 1;
140
141	/* New driver overlaps from the left. */
142	if (new_max >= old_min && new_max <= old_max) {
143	ret = -EBUSY;
144	goto out;
145	}
146
147	/* New driver overlaps from the right. */
148	if (new_min <= old_max && new_min >= old_min) {
149	ret = -EBUSY;
150	goto out;
151	}
152
153	if (new_min < old_min && new_max > old_max) {
154	ret = -EBUSY;
155	goto out;
156	}
157
158	}
159
160	cd->next = *cp;
161	*cp = cd;
162	mutex_unlock(&chrdevs_lock);
163	return cd;
164	out:
165	mutex_unlock(&chrdevs_lock);
166	kfree(cd);
167	return ERR_PTR(ret);
168	}
169
170	static struct char_device_struct *
171	__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
172	{
173	struct char_device_struct *cd = NULL, **cp;
174	int i = major_to_index(major);
175
176	mutex_lock(&chrdevs_lock);
177	for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
178	if ((*cp)->major == major &&
179	(*cp)->baseminor == baseminor &&
180	(*cp)->minorct == minorct)
181	break;
182	if (*cp) {
183	cd = *cp;
184	*cp = cd->next;
185	}
186	mutex_unlock(&chrdevs_lock);
187	return cd;
188	}
189
190	/**
191	* register_chrdev_region() - register a range of device numbers
192	* @from: the first in the desired range of device numbers; must include
193	* the major number.
194	* @count: the number of consecutive device numbers required
195	* @name: the name of the device or driver.
196	*
197	* Return value is zero on success, a negative error code on failure.
198	*/
199	int register_chrdev_region(dev_t from, unsigned count, const char *name)
200	{
201	struct char_device_struct *cd;
202	dev_t to = from + count;
203	dev_t n, next;
204
205	for (n = from; n < to; n = next) {
206	next = MKDEV(MAJOR(n)+1, 0);
207	if (next > to)
208	next = to;
209	cd = __register_chrdev_region(MAJOR(n), MINOR(n),
210	next - n, name);
211	if (IS_ERR(cd))
212	goto fail;
213	}
214	return 0;
215	fail:
216	to = n;
217	for (n = from; n < to; n = next) {
218	next = MKDEV(MAJOR(n)+1, 0);
219	kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
220	}
221	return PTR_ERR(cd);
222	}
223
224	/**
225	* alloc_chrdev_region() - register a range of char device numbers
226	* @dev: output parameter for first assigned number
227	* @baseminor: first of the requested range of minor numbers
228	* @count: the number of minor numbers required
229	* @name: the name of the associated device or driver
230	*
231	* Allocates a range of char device numbers. The major number will be
232	* chosen dynamically, and returned (along with the first minor number)
233	* in @dev. Returns zero or a negative error code.
234	*/
235	int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
236	const char *name)
237	{
238	struct char_device_struct *cd;
239	cd = __register_chrdev_region(0, baseminor, count, name);
240	if (IS_ERR(cd))
241	return PTR_ERR(cd);
242	*dev = MKDEV(cd->major, cd->baseminor);
243	return 0;
244	}
245
246	/**
247	* __register_chrdev() - create and register a cdev occupying a range of minors
248	* @major: major device number or 0 for dynamic allocation
249	* @baseminor: first of the requested range of minor numbers
250	* @count: the number of minor numbers required
251	* @name: name of this range of devices
252	* @fops: file operations associated with this devices
253	*
254	* If @major == 0 this functions will dynamically allocate a major and return
255	* its number.
256	*
257	* If @major > 0 this function will attempt to reserve a device with the given
258	* major number and will return zero on success.
259	*
260	* Returns a -ve errno on failure.
261	*
262	* The name of this device has nothing to do with the name of the device in
263	* /dev. It only helps to keep track of the different owners of devices. If
264	* your module name has only one type of devices it's ok to use e.g. the name
265	* of the module here.
266	*/
267	int __register_chrdev(unsigned int major, unsigned int baseminor,
268	unsigned int count, const char *name,
269	const struct file_operations *fops)
270	{
271	struct char_device_struct *cd;
272	struct cdev *cdev;
273	int err = -ENOMEM;
274
275	cd = __register_chrdev_region(major, baseminor, count, name);
276	if (IS_ERR(cd))
277	return PTR_ERR(cd);
278
279	cdev = cdev_alloc();
280	if (!cdev)
281	goto out2;
282
283	cdev->owner = fops->owner;
284	cdev->ops = fops;
285	kobject_set_name(&cdev->kobj, "%s", name);
286
287	err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
288	if (err)
289	goto out;
290
291	cd->cdev = cdev;
292
293	return major ? 0 : cd->major;
294	out:
295	kobject_put(&cdev->kobj);
296	out2:
297	kfree(__unregister_chrdev_region(cd->major, baseminor, count));
298	return err;
299	}
300
301	/**
302	* unregister_chrdev_region() - unregister a range of device numbers
303	* @from: the first in the range of numbers to unregister
304	* @count: the number of device numbers to unregister
305	*
306	* This function will unregister a range of @count device numbers,
307	* starting with @from. The caller should normally be the one who
308	* allocated those numbers in the first place...
309	*/
310	void unregister_chrdev_region(dev_t from, unsigned count)
311	{
312	dev_t to = from + count;
313	dev_t n, next;
314
315	for (n = from; n < to; n = next) {
316	next = MKDEV(MAJOR(n)+1, 0);
317	if (next > to)
318	next = to;
319	kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
320	}
321	}
322
323	/**
324	* __unregister_chrdev - unregister and destroy a cdev
325	* @major: major device number
326	* @baseminor: first of the range of minor numbers
327	* @count: the number of minor numbers this cdev is occupying
328	* @name: name of this range of devices
329	*
330	* Unregister and destroy the cdev occupying the region described by
331	* @major, @baseminor and @count. This function undoes what
332	* __register_chrdev() did.
333	*/
334	void __unregister_chrdev(unsigned int major, unsigned int baseminor,
335	unsigned int count, const char *name)
336	{
337	struct char_device_struct *cd;
338
339	cd = __unregister_chrdev_region(major, baseminor, count);
340	if (cd && cd->cdev)
341	cdev_del(cd->cdev);
342	kfree(cd);
343	}
344
345	static DEFINE_SPINLOCK(cdev_lock);
346
347	static struct kobject *cdev_get(struct cdev *p)
348	{
349	struct module *owner = p->owner;
350	struct kobject *kobj;
351
352	if (owner && !try_module_get(owner))
353	return NULL;
354	kobj = kobject_get(&p->kobj);
355	if (!kobj)
356	module_put(owner);
357	return kobj;
358	}
359
360	void cdev_put(struct cdev *p)
361	{
362	if (p) {
363	struct module *owner = p->owner;
364	kobject_put(&p->kobj);
365	module_put(owner);
366	}
367	}
368
369	/*
370	* Called every time a character special file is opened
371	*/
372	static int chrdev_open(struct inode *inode, struct file *filp)
373	{
374	const struct file_operations *fops;
375	struct cdev *p;
376	struct cdev *new = NULL;
377	int ret = 0;
378
379	spin_lock(&cdev_lock);
380	p = inode->i_cdev;
381	if (!p) {
382	struct kobject *kobj;
383	int idx;
384	spin_unlock(&cdev_lock);
385	kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
386	if (!kobj)
387	return -ENXIO;
388	new = container_of(kobj, struct cdev, kobj);
389	spin_lock(&cdev_lock);
390	/* Check i_cdev again in case somebody beat us to it while
391	we dropped the lock. */
392	p = inode->i_cdev;
393	if (!p) {
394	inode->i_cdev = p = new;
395	list_add(&inode->i_devices, &p->list);
396	new = NULL;
397	} else if (!cdev_get(p))
398	ret = -ENXIO;
399	} else if (!cdev_get(p))
400	ret = -ENXIO;
401	spin_unlock(&cdev_lock);
402	cdev_put(new);
403	if (ret)
404	return ret;
405
406	ret = -ENXIO;
407	fops = fops_get(p->ops);
408	if (!fops)
409	goto out_cdev_put;
410
411	replace_fops(filp, fops);
412	if (filp->f_op->open) {
413	ret = filp->f_op->open(inode, filp);
414	if (ret)
415	goto out_cdev_put;
416	}
417
418	return 0;
419
420	out_cdev_put:
421	cdev_put(p);
422	return ret;
423	}
424
425	void cd_forget(struct inode *inode)
426	{
427	spin_lock(&cdev_lock);
428	list_del_init(&inode->i_devices);
429	inode->i_cdev = NULL;
430	inode->i_mapping = &inode->i_data;
431	spin_unlock(&cdev_lock);
432	}
433
434	static void cdev_purge(struct cdev *cdev)
435	{
436	spin_lock(&cdev_lock);
437	while (!list_empty(&cdev->list)) {
438	struct inode *inode;
439	inode = container_of(cdev->list.next, struct inode, i_devices);
440	list_del_init(&inode->i_devices);
441	inode->i_cdev = NULL;
442	}
443	spin_unlock(&cdev_lock);
444	}
445
446	/*
447	* Dummy default file-operations: the only thing this does
448	* is contain the open that then fills in the correct operations
449	* depending on the special file...
450	*/
451	const struct file_operations def_chr_fops = {
452	.open = chrdev_open,
453	.llseek = noop_llseek,
454	};
455
456	static struct kobject *exact_match(dev_t dev, int *part, void *data)
457	{
458	struct cdev *p = data;
459	return &p->kobj;
460	}
461
462	static int exact_lock(dev_t dev, void *data)
463	{
464	struct cdev *p = data;
465	return cdev_get(p) ? 0 : -1;
466	}
467
468	/**
469	* cdev_add() - add a char device to the system
470	* @p: the cdev structure for the device
471	* @dev: the first device number for which this device is responsible
472	* @count: the number of consecutive minor numbers corresponding to this
473	* device
474	*
475	* cdev_add() adds the device represented by @p to the system, making it
476	* live immediately. A negative error code is returned on failure.
477	*/
478	int cdev_add(struct cdev *p, dev_t dev, unsigned count)
479	{
480	int error;
481
482	p->dev = dev;
483	p->count = count;
484
485	error = kobj_map(cdev_map, dev, count, NULL,
486	exact_match, exact_lock, p);
487	if (error)
488	return error;
489
490	kobject_get(p->kobj.parent);
491
492	return 0;
493	}
494
495	static void cdev_unmap(dev_t dev, unsigned count)
496	{
497	kobj_unmap(cdev_map, dev, count);
498	}
499
500	/**
501	* cdev_del() - remove a cdev from the system
502	* @p: the cdev structure to be removed
503	*
504	* cdev_del() removes @p from the system, possibly freeing the structure
505	* itself.
506	*/
507	void cdev_del(struct cdev *p)
508	{
509	cdev_unmap(p->dev, p->count);
510	kobject_put(&p->kobj);
511	}
512
513
514	static void cdev_default_release(struct kobject *kobj)
515	{
516	struct cdev *p = container_of(kobj, struct cdev, kobj);
517	struct kobject *parent = kobj->parent;
518
519	cdev_purge(p);
520	kobject_put(parent);
521	}
522
523	static void cdev_dynamic_release(struct kobject *kobj)
524	{
525	struct cdev *p = container_of(kobj, struct cdev, kobj);
526	struct kobject *parent = kobj->parent;
527
528	cdev_purge(p);
529	kfree(p);
530	kobject_put(parent);
531	}
532
533	static struct kobj_type ktype_cdev_default = {
534	.release = cdev_default_release,
535	};
536
537	static struct kobj_type ktype_cdev_dynamic = {
538	.release = cdev_dynamic_release,
539	};
540
541	/**
542	* cdev_alloc() - allocate a cdev structure
543	*
544	* Allocates and returns a cdev structure, or NULL on failure.
545	*/
546	struct cdev *cdev_alloc(void)
547	{
548	struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
549	if (p) {
550	INIT_LIST_HEAD(&p->list);
551	kobject_init(&p->kobj, &ktype_cdev_dynamic);
552	}
553	return p;
554	}
555
556	/**
557	* cdev_init() - initialize a cdev structure
558	* @cdev: the structure to initialize
559	* @fops: the file_operations for this device
560	*
561	* Initializes @cdev, remembering @fops, making it ready to add to the
562	* system with cdev_add().
563	*/
564	void cdev_init(struct cdev *cdev, const struct file_operations *fops)
565	{
566	memset(cdev, 0, sizeof *cdev);
567	INIT_LIST_HEAD(&cdev->list);
568	kobject_init(&cdev->kobj, &ktype_cdev_default);
569	cdev->ops = fops;
570	}
571
572	static struct kobject *base_probe(dev_t dev, int *part, void *data)
573	{
574	if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
575	/* Make old-style 2.4 aliases work */
576	request_module("char-major-%d", MAJOR(dev));
577	return NULL;
578	}
579
580	void __init chrdev_init(void)
581	{
582	cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
583	}
584
585
586	/* Let modules do char dev stuff */
587	EXPORT_SYMBOL(register_chrdev_region);
588	EXPORT_SYMBOL(unregister_chrdev_region);
589	EXPORT_SYMBOL(alloc_chrdev_region);
590	EXPORT_SYMBOL(cdev_init);
591	EXPORT_SYMBOL(cdev_alloc);
592	EXPORT_SYMBOL(cdev_del);
593	EXPORT_SYMBOL(cdev_add);
594	EXPORT_SYMBOL(__register_chrdev);
595	EXPORT_SYMBOL(__unregister_chrdev);
596